This invention relates to a fuel injection system for mixture-compressing, externally ignited internal combustion engines employing continuous fuel injection into the induction tube of the engine. The present invention relates, more particularly, to such a fuel injection system in which the induction tube contains therein a measuring member, as well as an arbitrarily actuatable throttle butterfly valve, the member and valve being disposed in sequence.
The measuring member in systems of the above-mentioned type moves as a function of the air flow rate through the indution tube and in opposition to a restoring force applied to the measuring member. In its motion, the measuring member sets the movable part of a valve, which is disposed in the fuel line, for metering a fuel quantity in proportion to the air flow rate. The restoring force for the measuring member is produced by pressurized fluid which acts continuously and at constant, but arbitrarily changeable pressure on a control slide which transmits the restoring force. The pressure is supplied through a control pressure circuit. The pressure within the circuit is changed by at least one pressure control valve which is controllable in dependence on motor parameters. The pressure control valve contains a heatable control element operating in dependence on temperature. The heatable control element may be embodied as a bimetallic spring which acts in opposition to the force of a spring within the pressure control valve when the engine operating temperatures are beneath the normal engine operating temperature. The control element is provided with an electric heating element.
The purpose of known fuel injection systems of the type discussed above is to create automatically a favorable fuel-air mixture for all operational conditions of internal combustion engines so as to permit complete fuel combustion, thereby preventing, or at least sharply reducing, the generation of toxic exhaust gases while maintaining the highest possible performance, for the least possible fuel consumption, of the internal combustion engine. In order to achieve this purpose, a fuel quantity which corresponds precisely to the requirement of each operational state of the internal combustion engine must be metered out.
In known fuel injection systems of this type, it is attempted to meter the fuel quantity out as nearly proportional as possible to the air quantity flowing through the induction tube. The ratio of the metered out fuel quantity to the air quantity may be changed by altering the restoring force acting on the measuring member as a function of motor parameters and by means of a pressure control valve.
It has been shown by experiment that during the warm-up phase of operation of an internal combustion engine, the fuel-air mixture may be set to be considerably leaner provided the engine is operating at relatively constant rpm and load, i.e., in steady operation, than if the throttle butterfly valve were opened suddenly.
Consequently, the emission of toxic material and the fuel consumption can both be lowered during the warm-up phase of the internal combustion engine in steady operation, by admitting a leaned out fuel-air mixture and by temporarily enriching the fuel-air mixture during any sudden opening of the throttle butterfly valve.